import java.util.LinkedList;
import java.util.Queue;

public class BinaryTree {
    static class TreeNode {
        public char val;
        public TreeNode left;//左孩子的引用
        public TreeNode right;//右孩子的引用

        public TreeNode(char val) {
            this.val = val;
        }
    }


    /**
     * 创建一棵二叉树 返回这棵树的根节点
     *
     * @return
     */
    public TreeNode createTree() {
        TreeNode A = new TreeNode('A');
        TreeNode B = new TreeNode('B');
        TreeNode C = new TreeNode('C');
        TreeNode D = new TreeNode('D');
        TreeNode E = new TreeNode('E');
        TreeNode F = new TreeNode('F');
        TreeNode G = new TreeNode('G');
        TreeNode H = new TreeNode('H');

        A.left = B;
        A.right = C;
        B.left = D;
        B.right = E;
        C.left = F;
        C.right = G;
        E.right = H;
        return A;//那么这个A就是根节点
    }

    // 前序遍历
    public void preOrder(TreeNode root) {
        if(root == null) return;
        //根
        System.out.print(root.val+" ");
        //左
        preOrder(root.left);
        preOrder(root.right);
    }

    // 中序遍历
    void inOrder(TreeNode root) {
        //左根右
        if(root == null) return;
        inOrder(root.left);
        System.out.print(root.val+" ");
        inOrder(root.right);
        //D B E H A F C G

    }

    // 后序遍历
    void postOrder(TreeNode root) {
        if(root == null) return;
        //左右根
        postOrder(root.left);
        postOrder(root.right);
        System.out.print(root.val + " ");
        //D H E B F G C A
    }

    public static int nodeSize;

    /**
     * 获取树中节点的个数：遍历思路
     */
    void size(TreeNode root) {
        if(root == null) return;
        nodeSize++;
        size(root.left);
        size(root.right);
    }

    /**
     * 获取节点的个数：子问题的思路
     *
     * @param root
     * @return
     */
    int size2(TreeNode root) {
        //左树节点+右树节点+ 1
        if(root == null) return 0;
        return size2(root.left) + size2(root.right) + 1;
    }


    /*
     获取叶子节点的个数：遍历思路
     */
    public static int leafSize = 0;

    void getLeafNodeCount1(TreeNode root) {
        if(root == null) return;
        if(root.left == null && root.right == null) {
            leafSize ++;
        }
        getLeafNodeCount1(root.left);
        getLeafNodeCount1(root.right);
    }

    /*
     获取叶子节点的个数：子问题
     */
    int getLeafNodeCount2(TreeNode root) {
        //子问题就是
        if(root == null) return 0;
        if (root.left == null && root.right == null) {
            return 1;
        }
        return getLeafNodeCount2(root.left) + getLeafNodeCount2(root.right);
    }

    /*
    获取第K层节点的个数
     */
    int getKLevelNodeCount(TreeNode root, int k) {
        if(root == null) return 0;

        if(k == 1) {
            return 1;
        }

        //第k层左树的节点+右树的节点
        return getKLevelNodeCount(root.left,k-1) + getKLevelNodeCount(root.right,k-1);
    }

    /*
     获取二叉树的高度
     时间复杂度：O(N)
     */
    int getHeight(TreeNode root) {
        //空树返回0
        if(root == null) return 0;
        //不是空树
        int leftHeight = getHeight(root.left);
        int rightHeight = getHeight(root.right);
        return Math.max(leftHeight,rightHeight) + 1;
    }


    // 检测值为value的元素是否存在
    TreeNode find(TreeNode root, char val) {
        if(root == null) return null;
        //不为空
        if(root.val == val) {
            return root;
        }
        find(root.left,val);
        find(root.right,val);
        return null;
    }

    //层序遍历
    //层序遍历就是一层一层的从左往右遍历
    void levelOrder(TreeNode root) {
        //创建队列
        Queue<TreeNode> queue = new LinkedList<>();
        //开始入队
        if(root != null) {
            queue.offer(root);
        }
        while(!queue.isEmpty()) {
            TreeNode top = queue.poll();
            System.out.print(top.val + " ");
            if(top.left != null) {
                queue.offer(top.left);
            }
            if(top.right != null) {
                queue.offer(top.right);
            }
        }


    }


    // 判断一棵树是不是完全二叉树
    boolean isCompleteTree(TreeNode root) {
        return true;
    }
}
